The present invention relates to the technical field of plastics or adhesives technology, more particularly to the adhesive bonding of edges, more particularly plastics edges, or edge bands. The present invention relates more particularly to a method for mounting edges, more particularly plastics edges, on materials, and also to the products produced in this way, and to the use thereof. The present invention further relates to a method for mounting adhesive layers, activatable by means of energy input, onto edge bands. The present invention likewise relates, moreover, to edge bands provided on at least one side with an adhesive layer which can be activated by means of energy input. Lastly, the present invention relates to the use in accordance with the invention of a composition for furnishing an edge band with an adhesive layer.
In the prior art there is a multiplicity of methods known for mounting edge bands onto the narrow faces of in particular panel-like workpieces. Typically in the prior art, edge bands are mounted onto the narrow faces of panel-like workpieces in through-travel machines, such as edging machines, for example, with the aid of edge gluing assemblies. Provision is generally made here for the narrow face of the workpiece to be furnished, immediately before the edge band is run up to it, with a hot-melt adhesive, more particularly so-called “hotmelts”. The mounting of edge bands in through-travel machines with hot-melt adhesive application taking place immediately prior to the run-up of the edge band is a cost-effective method which is also suitable for the manufacture of relatively large numbers of units. Nevertheless, this method entails a host of disadvantages.
For instance, the melting of the hot-melt adhesive is energy-intensive and leads overall to an increase in the operating costs; for example, up to half an hour elapses until an operating temperature of 150 to 210° C. is attained. Furthermore, energy is needed to heat the adhesives container, in order to maintain the adhesive in the liquid or application-ready state throughout the production process. Adhesive application is typically by means of spraying, jetting, rolling or knifecoating onto the workpiece.
Furthermore, the above-described method necessitates relatively large amounts of the adhesive. As a result, the adhesive joint, after solidifying, becomes more susceptible to penetration by dirt and moisture, and consequently, over the course of time, it is on the one hand possible for the adhesive bond to part, and on the other hand the adhesive joint is often of an unsatisfactory design from the standpoint of aesthetics.
In addition, the use of the adhesive in such large quantities leads to adhesive swelling out of the bondline in the course of subsequent pressing of the edge band onto the workpiece, and this leads to instances of fouling both of the workpiece and of the processing machine. In order to prevent this, the workpiece must be treated with release agents, in a cost-intensive and inconvenient operation, before the method is commenced.
In any case, the only hot-melt adhesives that can be processed in this way are those having relatively low molecular weights and relatively high melt indices, which, however, do not lead always to the desired bonding quality.
In view of the above-outlined disadvantages of this method, a search has been on for some considerable time for alternative possibilities for mounting edge bands on narrow faces of panel-like workpieces.
Other methods of the prior art attempt to avoid these advantages through provision of edge bands which have been precoated with adhesive and which allow subsequent mounting onto the narrow face at any desired point in time following application of adhesive. With precoated edge bands, adhesive application to the edge band and gluing onto the material take place separately from one another. It is normally necessary here for the adhesive layer to be (re)activated or melted before the edge band is mounted onto the material, so that the adhesive layer is once again in the tacky or adhesive state.
The (re)activation or melting of the adhesive layer of precoated edge bands for subsequent mounting of the edge band onto a material is typically accomplished by means of plasma treatment, hot air, or irradiation with infrared, UV, laser, or microwaves. Particularly in the case of the use of laser and microwave radiation, it is generally the case here that the adhesive layer comprises additives capable of energy absorption and/or conversion, such as mineral pigments, for example. The (re)activation process or the melting of the adhesive layer, however, is associated with numerous disadvantages.
Often there is only a weakly pronounced and/or poorly controllable transfer of energy to the adhesive, so that the heating is comparatively lengthy and/or unspecific. Furthermore, in view in particular of the poor controllability of the activation process, the edge band itself is often heated as well. Such heating, however, is detrimental to the quality of the edge band, since heating of the edge band may cause material damage, resulting in turn in a restriction on edge band materials to insensitive materials. Moreover, the additives needed for energy absorption and conversion, especially mineral pigments, are often very costly, leading overall to an increase in production costs. Moreover, such additives, especially mineral pigments, may lead to a deterioration in the bonding performance, particularly if they are employed in relatively large amounts; accordingly, their proportion is kept relatively low—but this often hinders homogeneous incorporation and hence homogeneous energy transfer.
A variety of methods are known in the prior art for producing edge bands precoated with adhesive. Although such methods do lead to an improvement in relation to the disadvantages specified above, and do enable, in particular, a more flexible regime, they are nevertheless unsatisfactory in numerous respects, especially in relation to the polymers that are to be used, and to the reactivation of the adhesive layer.
In the case of the production of precoated edge bands by means of coextrusion, such bands are generally produced as part of inline processes, with a subsequently activatable plastics layer or adhesive layer—in other words, the production of the edge band on the one hand and its furnishing with plastic or adhesive, on the other, take place, so to speak, contemporaneously. Coextrusion processes offer the advantage that on account of the high temperatures they allow even the processing of polymers having a particularly high molecular weight and low melt index. Using such polymers it is possible to generate particularly stable adhesive bonds.
As well as the aforementioned general disadvantages associated with aftercoated edge bands, however, coextrusion specifically is associated, furthermore, with numerous additional disadvantages. Coextrusion processes necessitate particularly high levels of investment in relation to the production line, which must always be individually tailored to the particular process. This technology is therefore economic only for large production runs or batches. Moreover, such processes also entail numerous disadvantages from a technical standpoint. The reason is that, with coextrusion processes, the direct joining of thermoplastic edge band to plastics layer and/or adhesive layer must take place without the use of an adhesion promoter. In the absence of the adhesion promoter layer, accordingly, sufficient adhesion can be achieved only between materials of the same kind. There is also no possibility of using, for example, resin-impregnated paper edges or veneer edges as edge bands, since only thermoplastic materials are extrudable. Overall, therefore, there is only a very limited selection of materials and a limited selection of materials combinations that can be used for the production of precoated edge bands by means of coextrusion.
It is possible, furthermore, to coat edge bands with a hot-melt adhesive or hotmelt as part of offline processes. With these processes, the edge band is first of all produced per se and only later is it coated with a subsequently activatable adhesive, by a toll coater or by a manufacturer of furniture parts, for example. Such offline processes overall offer good flexibility in relation to the edge materials that are to be coated, and the inexpensive process regime means that they also allow the equipping of small batches and production runs.
As well as the problems outlined above in relation to (re)activation, however, the production of aftercoated edge bands as part of offline processes is associated with further disadvantages. A particular problem is that the use of polymers with high molecular weights and low melt indices is not possible, since the high temperatures that are needed for such polymers are unachievable in offline operation. While it is possible to coat the edge tapes much more cost-effectively as part of such offline processes, the resultant adhesive bonds are nevertheless inferior in terms of service properties to the edge bands produced by means of coextrusion, and are comparable merely with the conventional gluing of edges using thermoplastic hotmelts, as described above.